Immune checkpoint inhibitors are monoclonal antibodies indicated for an increasing number of malignant diseases. These agents can cause specific side effects, which need to be anticipated while clear patterns of management need to be established. Immune checkpoint inhibitor-mediated gastrointestinal side effects, including diarrhea and colitis, occur in up to 30% of patients. Severe colitis can lead to severe dehydration or intestinal perforation. Endoscopic lesions and histopathological features of immune checkpoint inhibitor-induced colitis are similar to an inflammatory bowel disease (IBD) flare. Patients with immune checkpoint inhibitor-induced diarrhea and colitis are treated with corticosteroids. Infliximab can be used in cases of corticosteroid failure. Rectosigmoïdoscopy or colonoscopy should be performed when severe immune checkpoint inhibitor-induced colitis is suspected, but endoscopic investigations should not delay treatment. Specific patient education as well as co-operation between oncologists and gastroenterologists is essential.